Power management method and system for a battery powered aerosol-generating device

ABSTRACT

A method for controlling power supplied to an aerosol-generating element of an aerosol-generating device is provided, the aerosol-generating device including a controller and a battery configured to deliver power to the aerosol-generating element and to the controller, and the method including steps of: measuring at least one first characteristic of the battery, the first characteristic being a temperature or an internal resistance of the battery; and deactivating or disabling the aerosol-generating device if the measured temperature is less than a minimum temperature or the measured internal resistance of the battery is greater than a maximum internal resistance. A controller for an aerosol-generating device, and an aerosol-generating device, are also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of and claims benefitunder 35 U.S.C. § 120 to U.S. application Ser. No. 16/491,932, filed onSep. 6, 2019, which is a U.S. national stage application ofPCT/EP2018/055966, filed on Mar. 9, 2018, and claims benefit of priorityunder 35 U.S.C. § 119 to EP 17160953.0, filed on Mar. 14, 2017, theentire contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to battery powered aerosol-generating devices, andin particular to a method and system for controlling the supply of powerto an aerosol-generating element that improves the reliability of thedevice under different operating conditions.

DESCRIPTION OF THE RELATED ART

Typically, a battery powered aerosol-generating device, comprises anaerosol-generating element, such as a resistive heating element, that isconnected to a battery.

When an aerosol-generating device is first activated it is desirable tominimise the time taken for the device to deliver aerosol. Particularlyfor devices generating aerosol for inhalation, if the time taken todeliver a first puff is too long then users will become frustrated. In adevice that uses a resistive heater, this means increasing thetemperature of the heater as quickly as possible.

However, there are potential difficulties with simply delivering maximumpower to the aerosol-generating element at the outset.Aerosol-generating devices typically comprise a microcontroller unit(MCU) and various electronic components that need a minimum voltage tooperate correctly. Below this voltage, correct operation cannot beguaranteed. This is especially true for MCUs. But delivering maximumpower from the battery, especially when the battery is cold, can lead toinsufficient voltage at the MCU.

It is well known that drawing a high current from a battery reduces itsoutput voltage. This is due to the internal resistance of the battery.It is also known that at low temperature, the internal resistance of abattery is higher, thereby limiting the maximum discharge current. Inaddition, the output voltage of a battery is lower at low temperaturefor any given output battery current. And in those cases in which theaerosol-generating element is a resistive heater with a positivetemperature coefficient, the resistance of the heater will be at itslowest prior to activation and will increase with the temperature,leading to a greater voltage dropped across the internal resistance ofthe battery.

For these reasons, it is possible that applying maximum power at theoutset may cause the device to stop operating because the output voltagefrom the battery drops below a minimum voltage required for the MCU.

It would be desirable to be able to extract the maximum power from thebattery to make the device fully operational within the shortest amountof time, while ensuring that the output battery voltage is maintainedabove a minimum threshold voltage that ensures a correct operation ofthe MCU.

SUMMARY

To regulate the operation of the aerosol-generating device, the batterycan be dynamically connected to the aerosol-generating element so that aduty cycle of the current and voltage applied to the aerosol-generatingelement can be varied.

In a first aspect, there is provided a method for controlling powersupplied to an aerosol-generating element of an aerosol-generatingdevice, the aerosol-generating device comprising an aerosol-generatingelement, a control unit, and a battery for delivering power to theaerosol-generating element and to the control unit, the control unitconfigured to adjust a duty cycle of a current supplied from the batteryto the aerosol-generating element, wherein the method comprises thesteps of: measuring using a measuring unit, at least one firstcharacteristic of the battery; and adjusting, using the control unit, avalue of the duty cycle based on a predetermined rule which outputs avalue of duty cycle based on the measured at least one batterycharacteristic.

By controlling the duty cycle of the current supplied from the batteryin this way, as high a duty cycle as possible can be used whilemaintaining the voltage at the control unit at or above a minimumoperating voltage. The predetermined rule may be chosen to ensure thatthe voltage at the control unit exceeds a threshold voltage.

The at least one battery first characteristic may comprise a temperatureof the battery. The output voltage of a battery is affected bytemperature because its internal resistance is affected by temperature.A thermistor or other dedicated temperature sensor may be used to obtaina measure of the temperature of the battery. Alternatively, the at leastone battery characteristic may comprise a measure of battery age, such acount of charge and discharge cycles that the battery has completed. Acount of charge and discharge cycles may be recorded and stored in anmemory within the aerosol-generating device. Alternatively, the at leastone battery characteristic may comprise an internal resistance of thebattery or an impedance of the battery. The internal resistance of thebattery may be measured using well known techniques, such as the methoddescribed in WO2014/029880, Battery impedance measurement may be done byinjecting a small AC current into the battery and measuring theassociated AC voltage.

Advantageously, the steps of measuring and adjusting are carried outperiodically. As the battery discharges it will dissipate some heat as aresult of its internal resistance. This may result in a reduced internalresistance. The duty cycle may be adjusted periodically, for exampleevery 0.5 seconds, to account for the reducing internal resistance ofthe battery. In this way, the duty cycle may start at a low level andmay be progressively increased while ensuring that the control unitreceives sufficient voltage.

Advantageously, the predetermined rule defines a plurality of intervalsof values related to the at least one characteristic of the battery,each interval being associated with a respective duty cycle value, thestep of adjusting a value of the duty cycle comprising outputting theduty cycle value associated with an interval that includes a value ofthe measured at least one battery characteristic. The intervals ofvalues related to the at least one characteristic of the battery may besequential. The intervals of values related to the at least onecharacteristic of the battery may be non-overlapping.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with referenceto the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a device in accordance with anembodiment of the invention;

FIG. 2 illustrates the connection of the components of the deviceinvolved in a method in accordance with the invention;

FIG. 3 illustrates a set of sub-rules in accordance with an embodimentof the invention;

FIG. 4 is a flow diagram illustrating a control process according to anembodiment of the invention; and

FIG. 5 is an additional control process used in an embodiment of theinvention.

DETAILED DESCRIPTION

For example, in one embodiment, the at least one characteristic of thebattery is temperature and the predetermined rule comprises thefollowing intervals and associated duty cycle values:

1/ If the battery temperature is between −10° C. and −5° C., use a dutycycle value of 10%.

2/ If the battery temperature is between −5° C. and 0° C., use a dutycycle value of 20%.

3/ If the battery temperature is between 0° C. and 5° C., use a dutycycle value of 30%.

4/ If the battery temperature is between 5° C. and 10° C., use a dutycycle value of 40%.

5/ If the battery temperature is between 10° C. and 15° C., use a dutycycle value of 50%.

6/ If the battery temperature is between 15° C. and 20° C., use a dutycycle value of 60%.

7/ If the battery temperature is above 20° C., use any desired dutycycle.

With a handheld device it may be expected for the battery temperature torise during use, because of heat generated internally in the battery andheat generated by one or more heaters in the device, and from the userholding the device and transferring body heat to the battery.

The method may further comprise a step of measuring at least one secondcharacteristic of the aerosol-generating device and selecting the valueof a duty cycle based on a predetermined sub-rule and on the measuredvalue of at least one second characteristic of the aerosol-generatingdevice, wherein the predetermined sub-rule is selected from a group ofpredetermined sub-rules based on the measured at least one firstcharacteristic of the battery.

The steps of measuring at least one second characteristic and selectingthe value of duty cycle are carried out periodically. The duty cycle maybe adjusted periodically, for example every 0.5 seconds, to account fora changing value of the second characteristic of the aerosol-generatingelement. In this way, the duty cycle may start at a low level and may beprogressively increased while ensuring that the control unit receivessufficient voltage.

The at least one second characteristic of the aerosol-generating devicemay comprise an electrical resistance of the aerosol-generating element.An electrical resistance of the aerosol-generating element may changeduring use, as it may be temperature dependent. The aerosol-generatingelement may be a resistive heater. The at least one secondcharacteristic of the aerosol-generating device may comprise atemperature of the resistive heater. The electrical resistance of theresistive heater may be dependent on the temperature of the resistiveheater. Depending on the composition of the resistive heater, as theresistive heater heats up, the electrical resistance may increase forexample, resulting in a lower voltage drop across the internalresistance of the battery and thereby allowing for a greater duty cycleto be used.

The at least one second characteristic is different to the firstcharacteristic of the battery. The at least one second characteristicmay comprise a measure of battery age, such a count of charge anddischarge cycles that the battery has completed. A count of charge anddischarge cycles may be recorded and stored in an memory within theaerosol-generating device. Alternatively, the at least one secondcharacteristic may comprise an internal resistance of the battery or animpedance of the battery. Alternatively, if the temperature of thebattery is not used as the first characteristic of the battery, thetemperature of the battery may be used as the at least one secondcharacteristic.

The steps of measuring at least one second characteristic and selectingthe value of duty cycle may be carried out periodically until the atleast one second characteristic reaches a target value. In the exampleof a resistive heater, it may be desirable for the heater to reach atarget temperature or target range of temperatures for production of adesired aerosol but not to exceed that target. When the targettemperature is reached it is desirable to maintain the temperaturerather than to maximise a duty cycle of the current supplied to theheater. A varying duty cycle can be used for the purpose of regulatingthe temperature of a heater. The higher the duty cycle, the higher theaverage current delivered by the battery to the heating element, andhence the higher the heating element temperature. Of course, reducingthe duty cycle allows the contrary, e.g. to reduce the temperature ofthe heater.

The method may comprise monitoring a time since activation of thedevice, and if a target temperature is not reached within apredetermined time, deactivating or disabling the device.

The predetermined sub-rule may define a plurality of intervals of valuesrelated to the at least second characteristic of the aerosol-generatingdevice, each interval being associated with a respective duty cyclevalue. The step of adjusting a value of the duty cycle using the controlunit may comprise selecting the interval including the measured value ofat least one second characteristic of the aerosol-generating device. Theintervals of values related to the at least second characteristic of theaerosol-generating device may be sequential. The intervals of valuesrelated to the at least second characteristic of the aerosol-generatingdevice may be non-overlapping.

For example, if the first characteristic of the battery is batterytemperature and the second characteristic of the aerosol-generatingdevice is heating element resistance, and the battery temperature isdetermined to be −2° C., which is in the second range in the examplegiven above, then the sub-rule for that temperature range might be:

2.1/ If the heating element resistance is between 0.8 and 1 ohm, use aduty cycle of 20%

2.2/ If the heating element resistance is between 1 and 1.2 ohm, use aduty cycle of 30%

2.3/ If the heating element resistance is between 1.2 and 1.4 ohm, use aduty cycle of 40%

2.4/ If the heating element resistance is between 1.4 and 1.6 ohm, use aduty cycle of 50%

2.5/ If the heating element resistance is between 1.6 and 1.8 ohm, use aduty cycle of 60%

2.6/ If the heating element resistance is above 1.8 ohm, use any desiredduty cycle.

For each interval of values related to the at least one characteristicof the battery in the predetermined rule there may be a differentsub-rule.

The method may use further levels of sub-rules based on further measuredcharacteristics. In particular, the method may comprise a step ofmeasuring a third characteristic of the battery or aerosol-generatingdevice and selecting the value of a duty cycle based on a predeterminedsub-sub-rule and on the measured value of at least one thirdcharacteristic of the aerosol-generating device or battery, wherein thepredetermined sub-sub-rule is selected from a group of predeterminedsub-sub-rules based on a predetermined sub-rule, the measured secondcharacteristic and the measured at least one first characteristic of thebattery. For each interval of values of the second characteristic in asub-rule there may be a group of sub-sub-rules specifying a duty cycleassociated with different ranges of the third characteristic. Furtherlevels of rules may be used in a hierarchy of rules based on a pluralityof measured characteristics.

The method may further comprise periodically measuring an output batteryvoltage of the battery, calculating a rate of drop of output batteryvoltage based on measured output battery voltages, and reducing the dutycycle if the rate of drop of output battery voltage exceeds a thresholdlevel. This is advantageous because it arrests or slows the fall inoutput battery voltage to a level at which it is still possible toensure that that the control unit receives a minimum threshold voltage.For example, if, after a duty cycle of the current is increased inaccordance with the predetermined rule, the rate of drop of outputbattery voltage is determined to be such that the output battery voltagewould fall below a minimum operating voltage in only a few seconds,before the resistive heater could reach the target temperature, then theduty cycle could be reduced by 5%. There may be a different thresholdlevel of rate of drop of output battery voltage for each interval withinthe predetermined rule or sub-rules. The rate of drop of output batteryvoltage may be periodically calculated more frequently than the firstcharacteristic is measured. The rate of drop of output battery voltagemay be periodically calculated more frequently than the secondcharacteristic is measured.

The threshold level of rate of drop of output battery voltage may be setbased on an initial output battery voltage. In one example the thresholdlevel of rate of drop of output battery voltage could be defined by aminimum time it takes for the heater to increase its resistance to aparticular value, such as 1.6 Ohm for 3.2V battery, therefore drawing 2A of current. Then, the battery voltage should not drop below itsminimum value (for example 2.5V) before this minimum time. The minimumtime may be set as 5 seconds for example. If initial battery voltagevalue is 3.2V, then maximum rate of battery voltage drop would be:(3.2V−2.5V)/5=0.14V/s. Alternatively, the threshold level of rate ofdrop of output battery voltage could be specified to a set value,independent of initial output battery voltage, say 0.5V/s.

The method may further comprise subsequently increasing the duty cycleif the rate of drop of output battery voltage exceeds the threshold fora predetermined plurality of measurement cycles of output batteryvoltage.

The method may comprise deactivating or disabling the device if the dutycycle needs to be reduced below a minimum duty cycle.

In a second aspect, there is provided an aerosol-generating device,comprising: an aerosol-generating element; a control unit; a battery fordelivering a current to the aerosol-generating element and to thecontrol unit; and a measuring unit, connected to the control unit, formeasuring at least one first characteristic of the battery; wherein thecontrol unit is configured to adjust a duty cycle of the currentdelivered to the aerosol-generating element from the battery based on apredetermined rule which outputs a value of the duty cycle based on theat least one battery characteristic measured by the measuring unit.

The aerosol-generating device may comprise a non-volatile memory. Thenon-volatile memory may be part of the control unit. The non-volatilememory may store the predetermined rule.

The control unit may be configured to carry out a method in accordancewith the first aspect of the invention. In particular, the control unitmay be configured to use sub-rules as described in relation to the firstaspect of the invention. The control unit may be configured to measure arate of drop in output battery voltage as described in relation to thefirst aspect of the invention.

The control unit may comprise a switch. The control unit may beconfigured to adjust the duty cycle by operating the switch to turn thesupply of current to the aerosol-generating element on and off. Theswitch may be a transistor, such as metal-oxide-semiconductorfield-effect transistor (MOSFET).

The at least one characteristic of the battery may be batterytemperature. The measuring unit may comprise a temperature sensor.Alternatively, the at least one battery characteristic may comprise ameasure of battery age, such a count of charge and discharge cycles thatthe battery has completed. A count of charge and discharge cycles may berecorded and stored in an memory within the aerosol-generating device.Alternatively, the at least one battery characteristic may comprise aninternal resistance of the battery or an impedance of the battery. Theinternal resistance and impedance of the battery may be measured usingwell known techniques, such as the method described in WO2014/029880.

As used herein, an ‘aerosol-generating device’ relates to a device thatinteracts with an aerosol-forming substrate to generate an aerosol. Theaerosol-forming substrate may be part of an aerosol-generating article.An aerosol-generating device may be a device that interacts with anaerosol-forming substrate of an aerosol-generating article to generatean aerosol that is directly inhalable into a user's lungs thorough theuser's mouth. The aerosol generating element may be configured to heat,or otherwise atomise, an aerosol-forming substrate to form an aerosol.The aerosol-forming substrate may be fully or partially contained withinthe device.

The aerosol-forming substrate may be a solid aerosol-forming substrate.Alternatively, the aerosol-forming substrate may be a liquid or maycomprise both solid and liquid components. The aerosol-forming substratemay comprise a tobacco-containing material containing volatile tobaccoflavour compounds which are released from the substrate upon heating.Alternatively, the aerosol-forming substrate may comprise a non-tobaccomaterial. The aerosol-forming substrate may further comprise an aerosolformer. Examples of suitable aerosol formers are glycerine and propyleneglycol.

If the aerosol-forming substrate is a solid aerosol-forming substrate,the solid aerosol-forming substrate may comprise, for example, one ormore of: powder, granules, pellets, shreds, spaghettis, strips or sheetscontaining one or more of: herb leaf, tobacco leaf, fragments of tobaccoribs, reconstituted tobacco, homogenised tobacco, extruded tobacco, castleaf tobacco and expanded tobacco. The solid aerosol-forming substratemay be in loose form, or may be provided in a suitable container orcartridge. Optionally, the solid aerosol-forming substrate may containadditional tobacco or non-tobacco volatile flavour compounds, to bereleased upon heating of the substrate. The solid aerosol-formingsubstrate may also contain capsules that, for example, include theadditional tobacco or non-tobacco volatile flavour compounds and suchcapsules may melt during heating of the solid aerosol-forming substrate.

Optionally, the solid aerosol-forming substrate may be provided on orembedded in a thermally stable carrier. The carrier may take the form ofpowder, granules, pellets, shreds, spaghettis, strips or sheets.Alternatively, the carrier may be a tubular carrier having a thin layerof the solid substrate deposited on its inner surface, or on its outersurface, or on both its inner and outer surfaces. Such a tubular carriermay be formed of, for example, a paper, or paper like material, anon-woven carbon fibre mat, a low mass open mesh metallic screen, or aperforated metallic foil or any other thermally stable polymer matrix.

The solid aerosol-forming substrate may be deposited on the surface ofthe carrier in the form of, for example, a sheet, foam, gel or slurry.The solid aerosol-forming substrate may be deposited on the entiresurface of the carrier, or alternatively, may be deposited in a patternin order to provide a non-uniform flavour delivery during use.

Although reference is made to solid aerosol-forming substrates above, itwill be clear to one of ordinary skill in the art that other forms ofaerosol-forming substrate may be used with other embodiments. Forexample, the aerosol-forming substrate may be a liquid aerosol-formingsubstrate. If a liquid aerosol-forming substrate is provided, theaerosol-generating device preferably comprises means for retaining theliquid. For example, the liquid aerosol-forming substrate may beretained in a container. Alternatively or in addition, the liquidaerosol-forming substrate may be absorbed into a porous carriermaterial. The porous carrier material may be made from any suitableabsorbent plug or body, for example, a foamed metal or plasticsmaterial, polypropylene, terylene, nylon fibres or ceramic. The liquidaerosol-forming substrate may be retained in the porous carrier materialprior to use of the aerosol-generating device or alternatively, theliquid aerosol-forming substrate material may be released into theporous carrier material during, or immediately prior to use. Forexample, the liquid aerosol-forming substrate may be provided in acapsule. The shell of the capsule preferably melts upon heating andreleases the liquid aerosol-forming substrate into the porous carriermaterial. The capsule may optionally contain a solid in combination withthe liquid. Alternatively, the carrier may be a non-woven fabric orfibre bundle into which tobacco components have been incorporated. Thenon-woven fabric or fibre bundle may comprise, for example, carbonfibres, natural cellulose fibres, or cellulose derivative fibres.

During operation, the aerosol-forming substrate may be completelycontained within the aerosol-generating device. In that case, a user maypuff on a mouthpiece of the aerosol-generating device. Alternatively,during operation an aerosol-forming article containing theaerosol-forming substrate may be partially contained within theaerosol-generating device. In that case, the user may puff directly onthe aerosol-forming article.

The aerosol-forming article may be substantially cylindrical in shape.The aerosol-forming article may be substantially elongate. Theaerosol-forming article may have a length and a circumferencesubstantially perpendicular to the length. The aerosol-forming substratemay be substantially cylindrical in shape. The aerosol-forming substratemay be substantially elongate. The aerosol-forming substrate may alsohave a length and a circumference substantially perpendicular to thelength.

The aerosol-forming article may have a total length betweenapproximately 30 mm and approximately 100 mm. The aerosol-formingarticle may have an external diameter between approximately 5 mm andapproximately 12 mm. The aerosol-forming article may comprise a filterplug. The filter plug may be located at the downstream end of theaerosol-forming article. The filter plug may be a cellulose acetatefilter plug. The filter plug is approximately 7 mm in length in oneembodiment, but may have a length of between approximately 5 mm toapproximately 10 mm.

In one embodiment, the aerosol-forming article has a total length ofapproximately 45 mm. The aerosol-forming article may have an externaldiameter of approximately 7.2 mm. Further, the aerosol-forming substratemay have a length of approximately 10 mm. Alternatively, theaerosol-forming substrate may have a length of approximately 12 mm.Further, the diameter of the aerosol-forming substrate may be betweenapproximately 5 mm and approximately 12 mm. The aerosol-forming articlemay comprise an outer paper wrapper. Further, the aerosol-formingarticle may comprise a separation between the aerosol-forming substrateand the filter plug. The separation may be approximately 18 mm, but maybe in the range of approximately 5 mm to approximately 25 mm.

The aerosol-generating element may be a resistive heater. The at leastone second characteristic of the aerosol-generating element may be atemperature or an electrical resistance of the resistive heater.

The resistive heater may comprise an electrically resistive material.Suitable electrically resistive materials include but are not limitedto: semiconductors such as doped ceramics, electrically “conductive”ceramics (such as, for example, molybdenum disilicide), carbon,graphite, metals, metal alloys and composite materials made of a ceramicmaterial and a metallic material. Such composite materials may comprisedoped or undoped ceramics. Examples of suitable doped ceramics includedoped silicon carbides. Examples of suitable metals include titanium,zirconium, tantalum platinum, gold and silver. Examples of suitablemetal alloys include stainless steel, nickel-, cobalt-, chromium-,aluminium- titanium- zirconium-, hafnium-, niobium-, molybdenum-,tantalum-, tungsten-, tin-, gallium-, manganese-, gold- andiron-containing alloys, and super-alloys based on nickel, iron, cobalt,stainless steel, Timetal® and iron-manganese-aluminium based alloys. Incomposite materials, the electrically resistive material may optionallybe embedded in, encapsulated or coated with an insulating material orvice-versa, depending on the kinetics of energy transfer and theexternal physicochemical properties required.

The aerosol generating device may comprise an internal resistive heateror an external resistive heater, or both internal and external resistiveheaters, where “internal” and “external” refer to the aerosol-formingsubstrate. An internal resistive heater may take any suitable form. Forexample, an internal resistive heater may take the form of a heatingblade. Alternatively, the internal resistive heater may take the form ofa casing or substrate having different electro-conductive portions, oran electrically resistive metallic tube. Alternatively, the internalresistive heater may be one or more heating needles or rods that runthrough the centre of the aerosol-forming substrate. Other alternativesinclude a heating wire or filament, for example a Ni—Cr(Nickel-Chromium), platinum, tungsten or alloy wire or a heating plate.Optionally, the internal resistive heater may be deposited in or on arigid carrier material. In one such embodiment, the electricallyresistive heater may be formed using a metal having a definedrelationship between temperature and resistivity. In such an exemplarydevice, the metal may be formed as a track on a suitable insulatingmaterial, such as ceramic material, and then sandwiched in anotherinsulating material, such as a glass. Heaters formed in this manner maybe used to both heat and monitor the temperature of the heating elementsduring operation.

An external resistive heater may take any suitable form. For example, anexternal resistive heater may take the form of one or more flexibleheating foils on a dielectric substrate, such as polyimide. The flexibleheating foils can be shaped to conform to the perimeter of the substratereceiving cavity. Alternatively, an external heating element may takethe form of a metallic grid or grids, a flexible printed circuit board,a moulded interconnect device (MID), ceramic heater, flexible carbonfibre heater or may be formed using a coating technique, such as plasmavapour deposition, on a suitable shaped substrate. An external resistiveheater may also be formed using a metal having a defined relationshipbetween temperature and resistivity. In such an exemplary device, themetal may be formed as a track between two layers of suitable insulatingmaterials. An external resistive heater formed in this manner may beused to both heat and monitor the temperature of the external heatingelement during operation.

The resistive heater advantageously heats the aerosol-forming substrateby means of conduction. The heating element may be at least partially incontact with the substrate, or the carrier on which the substrate isdeposited. Alternatively, the heat from either an internal or externalheater may be conducted to the substrate by means of a heat conductiveelement.

The battery may be a rechargeable battery. The battery may be a lithiumion battery, for example a Lithium-Cobalt, a Lithium-Iron-Phosphate,Lithium Titanate or a Lithium-Polymer battery. Alternatively, thebattery may another form of rechargeable battery, such as a Nickel-metalhydride battery or a Nickel cadmium battery.

The measuring unit may be integral with the battery or may be located onor in a battery housing.

The control unit may comprise a microcontroller unit (MCU). The controlunit may be programmable. The control unit may comprise a switchconnected to the battery in series with the aerosol-generating element.

The device is preferably a portable or handheld device that iscomfortable to hold between the fingers of a single hand. The device maybe substantially cylindrical in shape and has a length of between 70 and120 mm. The maximum diameter of the device is preferably between 10 and20 mm. In one embodiment the device has a polygonal cross section andhas a protruding button formed on one face. In this embodiment, thediameter of the device is between 12.7 and 13.65 mm taken from a flatface to an opposing flat face; between 13.4 and 14.2 taken from an edgeto an opposing edge (i.e., from the intersection of two faces on oneside of the device to a corresponding intersection on the other side),and between 14.2 and 15 mm taken from a top of the button to an opposingbottom flat face.

The aerosol-generating device may be an electrically heatedaerosol-forming device. In a third aspect of the invention, there isprovided a computer program which, when run on programmable electriccircuitry in a control unit of an electrically operated aerosolgenerating device, the aerosol-generating device comprising anaerosol-generating element, and a battery for delivering power to theaerosol-generating element and to the control unit, causes theprogrammable electric circuitry to perform a method according to thefirst aspect of the invention.

Although the disclosure has been described by reference to differentaspects, it should be clear that features described in relation to oneaspect of the disclosure may be applied to the other aspects of thedisclosure.

In FIG. 1 , the components of an embodiment of an electrically heatedaerosol generating device 1 are shown in a simplified manner. Theelements of the electrically heated aerosol generating device 1 are notdrawn to scale in FIG. 1 . Elements that are not relevant for theunderstanding of this embodiment have been omitted to simplify FIG. 1 .

The electrically heated aerosol generating device 1 comprises a housing10 and an aerosol-forming substrate 12, for example a aerosol-formingarticle such as a cigarette. The aerosol-forming substrate 12 is pushedinside the housing 10 to come into thermal proximity with a heater 4. Inthis example, the heater is a blade that extends into theaerosol-forming substrate The aerosol-forming substrate 12 will releasea range of volatile compounds at different temperatures. By controllingthe maximum operation temperature of the heater to be below the releasetemperature of some of the volatile compounds, the release or formationof these smoke constituents can be avoided. Typically theaerosol-forming substrate is heated to a temperature of between 250 and450 degrees centigrade. Within the housing 10 there is an electricbattery 2, for example a rechargeable lithium ion battery. A controlunit 3 is connected to the heating element 2, the electric battery 2,and a user interface 6, for example a button or display. This type ofsystem is described in EP2800486 for example.

The control unit 3 controls the power supplied to the heating element 4in order to regulate its temperature by varying a duty cycle of thecurrent. FIG. 2 illustrates the connection of battery, control unit andresistive heater in the device of FIG. 1 .

The battery 2 is illustrated as an ideal battery 21 together with aninternal resistance 22. The battery is connected to the resistive heater4 through a control unit. The control unit comprises an microprocessorunit (MCU) 20 and a switch 23. The MCU controls the operation of theswitch to control a duty cycle of the current delivered to the heater 4.The MCU 20 comprises a non-volatile memory 27.

The device also comprises a temperature sensor 25, positioned to measurea temperature of the battery 2. For example, the temperature sensor maybe a thermistor to provide an analogue measurement of temperature, or adigital temperature sensor, such as LM75ADP from NXP. An output of thetemperature sensor 25 is connected to the MCU 20. The temperature of thebattery as measured by the temperature sensor 25 is used to control theoperation of the switch 23 based on at least one rule stored in thenon-volatile memory 27, as will be described.

The device may be activated by a user using the user interface 6. Whenthe device is activated electrical current is delivered from the batteryto the heater through the switch 23.

Ideally the heater is raised to a target temperature as quickly aspossible after activation while ensuring that the MCU receives asufficient voltage for proper function. At the outset, when the batteryis cool, it will have a relatively high internal resistance, meaningthat a greater proportion of the battery voltage will be dropped acrossthe internal resistance that after the battery has heated up. This meansthat when the battery is cooler, a lower duty cycle for the current isdesirable to ensure that the MCU receives at least a minimum operatingvoltage.

The voltage received by the MCU is also influenced by the resistance ofthe heater 4. The resistance of the heater 4 will typically vary duringoperation of the device, as it heats up. The heater may be formed from amaterial that has a significant variation of resistance with temperatureso that the resistance of the heater can be used as a measure of thetemperature of the heater for heater temperature control. The heater inthis example has a positive temperature coefficient so that theresistance of the heater increases as the heater temperature increases.

The MCU may be configured to measure the electrical resistance of theheater 4. This may be achieved by using a shunt resistor (with a verylow resistance) in series with the heater 4. The current through theshunt resistor, which is also the current through the heater, can bemeasured using an amplifier connected in parallel to the shunt resistor.The voltage across the heater can be measured directly and theresistance of the heater then calculated using Ohm's law. This is awell-known measurement technique.

The MCU controls the operation of the switch according to a rule storedin the memory of the MCU. FIG. 3 illustrates one example of a rule 30that the MCU could use. The rule relates a measured temperature of thebattery T_(bat) and a measured electrical resistance of the heater R_(h)to an output duty cycle. The rule comprises a plurality of sub-rules,each associated with a range of battery temperatures. The ranges ofbattery temperatures are sequential but do not overlap with each other.Within each sub-rule there is a plurality of duty cycles, eachassociated with a distinct range of heater resistances. The ranges ofheater resistances are sequential but do not overlap with each other. Todetermine which duty cycle to use, the MCU first selects a sub-ruleassociated with a range of battery temperatures in which the measuredbattery temperature 31 falls. In the example illustrated in FIG. 3 ,this is Range 2, covering temperatures from T2 to T3, as illustrated bythe dotted line box 32. The MCU then selects a duty cycle from withinthe sub-rule associated with Range 2. The duty cycle chosen is the dutycycle associated with the range of heater resistances in which themeasured heater resistance 33 falls. In the example shown in FIG. 3 , itis duty cycle DC8 associated with resistance range R_(h5) to R_(h6), asillustrated by the dotted line box 34. The output from the rule 30 istherefore DC8, as shown by box 36.

Instead of using heater resistance in the rule, another parameter, suchas heater temperature could be used. The device may include atemperature sensor close to the heater. The output of the temperaturesensor would be connected to the MCU.

The number of ranges and sub-ranges can be chosen according toparticular design requirements and according to the construction of theheater 4. The example shown in FIG. 4 comprises four ranges of batterytemperature and four ranges of heater resistance. In another embodiment,there are seven ranges of battery temperature as follows:

1/ −10° C. to −5° C.

2/ −5° C. to 0° C.

3/ 0° C. to 5° C.

4/ 5° C. to 10° C.

5/ 10° C. to 15° C.

6/ 15° C. to 20° C.

7/ above 20° C.

And there are six ranges of heater resistance used in each sub-rule, asfollows:

1/ 0.8 to 1 ohm

2/ 1 to 1.2 ohm

3/ 1.2 to 1.4 ohm

4/ 1.4 to 1.6 ohm

5/ 1.6 to 1.8 ohm

6/ above 1.8 ohm.

The value of the duty cycle associated with each range in each sub-ruleshould be chosen to ensure that the MCU will always receive at least aminimum operating voltage required for proper function of the MCU. Ifthe battery temperature is below −10° C. the device is disabled.

The process for adjusting the duty cycle of the current delivered to theheater is carried out periodically, for example every 0.5 secondsfollowing activation of the device, until the heater reaches a targettemperature or target resistance. So every 0.5 seconds a new sub-rulemay be applied, depending on changes in the battery temperature andheater resistance.

If the heater does not reach a target temperature, for example 350° C.,with a fixed time, for example 30 seconds, the heating process isstopped. In this situation, the battery cannot deliver enough power tothe heater. This may be because the battery is old.

FIG. 4 is a flow chart showing an example control process using a ruleof the type described above. The device is activated in step 40. In afirst step 41 following activation the temperature of the battery ismeasured. Then, in step 42, a duty cycle for the current is selectedbased on the battery temperature. At this stage, before any current hasbeen applied to the heater it is assumed that the heater resistance isat a maximum value. In step 43 the MCU operates the switch in accordancewith the selected duty cycle to deliver current to the heater. This dutycycle is maintained for a predetermined period, such as 0.5 seconds.During this period the electrical resistance of the heater is measured,in step 44. In step 45 the measured electrical resistance is compared toa target resistance, corresponding to target heater temperature. If theheater resistance is equal to or greater than the target resistance thenthe process ends at step 46. If the heater resistance is less than thetarget resistance, indicating that the heater has not reached the targettemperature, then the process returns to step 41 when the batterytemperature is measured again. In step 42 the duty cycle is againselected using the predetermined rule, this time based on both batterytemperature and heater resistance. The process is repeated until thetarget resistance is achieved or until 30 seconds after activation,whichever occurs sooner.

The benefit of the process descried with reference to FIG. 4 is that itallows the maximum power to be extracted from the battery to heat theheater quickly, while keeping the battery voltage above a pre-definedthreshold with a sufficient safety margin. The duty cycle is started ata low value and progressively raised as quickly as allowed, as theheater resistance rises and the battery temperature rises. This meansthat the heater is quickly but reliably heated to its targettemperature.

FIG. 5 illustrates an additional control process that may be used tofurther ensure that the MCU always receives a sufficient voltage duringoperation of the device.

For the process of FIG. 5 , a maximum limit for the rate of outputbattery voltage drop is set, referred to here as the limit of rate ofvoltage drop. The limit of rate of voltage drop may be different fordifferent sub-rules or different measured battery voltages.

If the rate of voltage drop is greater than the limit of rate of voltagedrop, then the duty cycle of the current is reduced in order to slow therate of voltage drop.

The process shown in FIG. 5 starts with step 50, in which the batteryvoltage is measured. In step 51 a rate of drop of battery voltage iscalculated from the measured battery voltage and from measurements ofbattery voltage made in previous cycles of the process. In step 52 theMCU determines if the rate of drop of battery voltage is greater thanthe threshold (or if the rate of change of battery voltage is lower thanthe threshold). If the rate of drop of battery voltage is greater thanthe limit, then in step 53 the duty cycle is reduced by a predeterminedamount. The process then returns to step 50. For example if the currentduty cycle is 20% then a maximum rate of battery voltage drop of 0.5V/scould be defined. The rate of battery voltage drop would be measuredevery 200 ms interval, for example. If, in step 52 the rate of drop ofbattery voltage is greater than the threshold, the duty cycle would bereduced from 20% to 15%, and then further reduced from 15% to 10% ifrate of battery drop is still more than 0.5V/s in the next cycle, afterfurther 200 ms. A lower limit on the duty cycle of 5% could be set. Ifthe process requires the duty cycle to be reduced from 5%, then thedevice may be deactivated.

This process is beneficial as it prevents the voltage at the MCUdropping below a minimum operational voltage as a result of a rapidvoltage drop following a change in duty cycle. For example, if theoutput battery voltage starts at 3.4V, and the battery voltage drops ata rate of 0.5V/s, a voltage of 2.4V would be reached in less than 2seconds. This voltage is below the 2.5V minimum operating voltage andwould be reached in only 2 seconds, which is not enough time to heat upthe heater significantly.

The process of FIG. 5 also allows for duty cycle to be increasedfollowing a reduction if the rate of battery voltage drop increases.However the process requires the rate of voltage drop to be lower thanthe threshold for two cycles before the duty cycle is increased. To dothis, a count is incremented for every cycle after an initial duty cycledrop in which the rate of drop of battery voltage is lower than thelimit. If the rate of voltage drop is lower than the limit the count isincremented by one in step 54. If the rate of voltage drop is higherthan the limit the count is reset to zero in step 53. Only if the countis determined to be equal to two in step 55 is the duty cycle increasedin step 56. Otherwise the duty cycle is unchanged. In the exampledescribed, this means that the rate of drop of battery voltage must beless than 0.5V/s for 400 ms, before going back up by step of 5% (insteadof 200 ms when going down by step of 5%). This hysteresis providesstability to the system.

There may be other variables that affect the ideal duty cycle to use,such as the age of the battery (which may be measured as a count of thenumber of charge and discharge cycles it has performed), the internalresistance of the battery or the internal impedance of the battery. Oneor more of these variables may be used as the first or secondcharacteristic. Alternatively, in order to provide finer control of dutycycle, it is possible to use a further tier or tiers of rules within thehierarchy of rules and sub-rules based on one or more of thesevariables. For example, a third characteristic may be a count of thecharge and discharge cycles that the battery has been through. The countof charge and discharge cycles that the battery has been through may berecorded and stored in a memory within the control unit. Modifying theembodiment of FIG. 3 , each sub-rule, based on heater resistance,instead of specifying a duty cycle to use for each measured heaterresistance, may specify a plurality of sub-sub-rules to use for eachvalue of heater resistance. Each sub-sub-rule may specify a duty cycleto use for a range of values for the count of charge and dischargecycles that the battery has been through. The sub-sub-rule used isselected based on the stored count of charge and discharge cycles in thememory of the control unit. In this way, the duty cycle is selectedbased on the temperature of the battery, the resistance of the heaterand the number of charge and discharge cycles completed by the battery.The order in which the measured characteristics are assigned to therules, sub-rules and sub-sub-rules may be varied.

The invention claimed is:
 1. A method for controlling power supplied toan aerosol-generating element of an aerosol-generating device, theaerosol-generating device comprising a control unit and a batteryconfigured to deliver power to the aerosol-generating element and to thecontrol unit, and the method comprising steps of: measuring at least onefirst characteristic of the battery, the first characteristic being atemperature or an internal resistance of the battery; and deactivatingor disabling the aerosol-generating device if the measured temperatureis less than a minimum temperature or the measured internal resistanceof the battery is greater than a maximum internal resistance.
 2. Themethod according to claim 1, wherein the minimum temperature is −10° C.3. The method according to claim 1, wherein the control unit isconfigured to adjust a duty cycle of a current supplied from the batteryto the aerosol-generating element.
 4. The method according to claim 3,further comprising the step of adjusting, using the control unit, theduty cycle of the current supplied from the battery to theaerosol-generating element.
 5. The method according to claim 4, whereinthe duty cycle of the current supplied from the battery to theaerosol-generating element is adjusted to maintain a voltage at thecontrol unit at or above a minimum operating voltage.
 6. The methodaccording to claim 3, further comprising the step of adjusting, usingthe control unit, the current supplied from the battery to theaerosol-generating element based on a predetermined rule.
 7. The methodaccording to claim 6, wherein the duty cycle of the current is adjustedbased on the predetermined rule.
 8. The method according to claim 6,wherein the predetermined rule comprises outputting a value of the dutycycle based on the measured at least one first characteristic of thebattery.
 9. The method according to claim 6, wherein the predeterminedrule comprises outputting a duty cycle value of 0% if the measuredtemperature of the battery is less than the minimum temperature.
 10. Themethod according to claim 1, further comprising the step of measuring asecond characteristic of the aerosol-generating device that is at leastone of: a measure of battery age, an electrical resistance or atemperature of the aerosol-generating element, and a rate of drop ofoutput battery voltage.
 11. The method according to claim 10, whereinthe control unit is configured to adjust a duty cycle of a currentsupplied from the battery to the aerosol-generating element, wherein themethod further comprises adjusting, using the control unit, a currentsupplied from the battery to the aerosol-generating element based on apredetermined rule, and wherein the predetermined rule comprisesoutputting a value of the duty cycle based on the measured secondcharacteristic.
 12. The method according to claim 1, wherein themeasuring comprises using a temperature sensor to measure thetemperature of the battery.
 13. The method according to claim 12,wherein the temperature sensor is a thermistor.
 14. The method accordingto claim 1, wherein the first characteristic of the battery is theinternal resistance of the battery and the step of measuring theinternal resistance comprises passing an alternating current into thebattery and measuring an associated voltage of the alternating current.15. The method according to claim 11, wherein the steps of measuring andadjusting are carried out periodically.
 16. The method according toclaim 11, wherein the steps of measuring and adjusting are carried outevery 0.5 seconds.
 17. The method according to claim 1, wherein theaerosol-generating device comprises the aerosol-generating element. 18.A control unit for an aerosol-generating device, comprising: a batteryconfigured to deliver a current to an aerosol-generating element and tothe control unit; and a measuring unit for measuring at least one firstcharacteristic of the battery, the first characteristic being atemperature or an internal resistance of the battery, wherein thecontrol unit is configured to deactivate or to disable theaerosol-generating device if the measured temperature of the battery isless than a minimum temperature or the measured internal resistance ofthe battery is greater than a maximum internal resistance.
 19. Anaerosol-generating device, comprising: a control unit according to claim18; a battery configured to deliver a current to an aerosol-generatingelement and to the control unit; and a measuring unit for measuring atleast one first characteristic of the battery, the first characteristicbeing a temperature or an internal resistance of the battery.
 20. Theaerosol-generating device according to claim 19, wherein the battery isa lithium ion battery.